Prepared by:

Dr. Dulari Hansdah

Assistant Professor

Department of Mechanical Engineering

NIT Jamshedpur

Heat Engine A heat engine is a device which transforms the chemical energy of a fuel into thermal

energy and uses this energy to produce mechanical work.

useful devices since the 17th century, classic example of a heat engine is steam engine

Classified into two types: External combustion engine and Internal Combustion

engine

External Combustion Engine

Products of combustion of air and fuel transfer heat to a second fluid which is the

working fluid of the cycle.

Source: M.L. Mathur and R.P. Sharma, “Internal Combustion Engine”, Text book

Engine type Reciprocating or

rotary type

Maximum size in

kW

Principal Use

Steam Engine Reciprocating 4000 Locomotives, ships

Steam Turbine Rotary 5,00,000 Electric power, large marine

Stirling or hot air engine Reciprocating 800 Experimental, power in space,

vehicles

Closed cycle gas turbine Rotary 80,000 Electric power, marine

Fig: Steam engine details

In 1690 the first steam piston engine was developed by French physicist Denis Papin

for pumping water.

Steam engines are classified into single acting and double acting steam engine, simple

and compound steam engine, low speed and high speed steam engine

It is steam driven rotary engine. Oldest

prime mover technology in which

potential energy is converted into kinetic

energy and then to mechanical energy

Wide application in CHP (combined heat

and power) plant

Thermodynamic cycle is “Rankine cycle”

Capacities varies from 50 kWs to

hundreds of MWs

Fig: Steam Turbine in steam

power plant

Working of turbine wholly depends upon the dynamic action of the steam

Mechanical work is obtain through expansion Turbine. Expansion takes place

through a series of fixed blades (nozzles) and moving blades

In each row fixed blade and moving blades are called stage

Classification of Steam Turbine:

Steam Turbine

Impulse Steam

Turbine

Reaction Steam

Turbine

Simple Steam Turbine

(de Laval)

Compound Steam

Turbine

Velocity compounded

(Curtis)

Pressure compounded

(Rateau)

Steam turbine operation adopt two concepts, which may be used either separately

or together.

In an impulse turbine the steam is expanded through nozzles

so that it reaches a high velocity. The high-velocity, low-pressure

jet of steam is then directed against the blades of a spinning wheel,

where the steam's kinetic energy is extracted while performing

work. Only low-velocity, low-pressure steam leaves the turbine.

It’s pressure does not alter as it moves over the blades.

In a reaction turbine the steam expands through a series

of stages, each of which has a ring of curved stationary

blades and a ring of curved rotating blades. In the rotating

section the steam expands partially while providing a

reactive force in the tangential direction to turn the

turbine wheel. There is gradual fall in the pressure during

expansion below the atmospheric pressure.

One of the hot air engines, invented by Robert Stirling (1790-

1878)

Aim to replace the steam engine in which frequent explosion

caused by unstable high pressure

It is operated by a cyclic compression and expansion of

air or other gas (the working fluid) at different temperatures

The working gas is generally compressed in the colder portion

of the engine and expanded in the hotter portion resulting

in a net conversion of heat into work

It is closed-cycle regenerative heat engine with a permanently

gaseous working fluid

practical use largely confined to low-power domestic

applications for over a century

Stirling engines can be economical, quieter, safer and less

maintenance-freeFig: Simple Stirling engine

3 major types: alpha, beta and gamma Stirling engine, distinguished by the way they

move the air between the hot and cold areas

Fig: Alpha Stirling engineFig: Beta Stirling engine

Fig: Gamma Stirling engine

Two cylinders, expansion cylinder

(hot) maintains high temp. and

compression cylinder (blue) is

cooled. The passage between the

two cylinders contains the

regenerator.

Beta-type Stirling engine. There is

only one cylinder, hot at one end and

cold at the other. A loose-fitting

displacer shunts the air between the

hot and cold ends of the cylinder. A

power piston at the open end of the

cylinder drives the flywheel.

Simply a Stirling beta engine in

which the power piston is not

mounted coaxially with the

displacer piston but in a separate

cylinder.

Closed-cycle gas turbine uses a gas (e.g. air, nitrogen, helium, argon etc.) for the working

fluid as part of a closed thermodynamic system. Heat is supplied from an external source.

No corrosion and accumulation of deposits of

carbon or tar on the blade or nozzles of the

Turbine. Hence less internal cleaning is

required

Higher turbine efficiency

Waste heat can be utilized for hot water supply

for industrial or domestic purpose

More complicated and costly

Coolant is required for cooling

Historical Development:

1680: Huygens Gunpowder engine

Christian Huygens Huygens Gun powder engine

internal combustion engine that was to be fueled with gunpowder

consists of vertical cylinder, sliding fit type of piston

Explosion of powder drove the piston on its upward stroke and useful work was

produced on the downward stroke of the piston

1860: Lenoir Engine

Jean Joseph Etienne Lenoir Lenoir engine

Non-compression combustion gas engine

similar to a double acting steam engine in which steam is replaced by the gas

formed by the combustion of the charge of air-gas mixture

used in modern pulse jet engine

Low efficiency due to low expansion ratio

1866: Free Piston Otto-Langen Engine

Free Piston Otto-Langen engine

consist of piston without any crankshaft and free to move vertically outwards during

the explosion and expansion stroke

inertia of flywheel raised the piston from bottom position and inducted fresh air-gas

charge

Thermal efficiency is higher than that of the Lenoir engine but its operation is noisy

1876: Four Stroke Cycle (Otto Cycle)

Nikolaus August Otto Otto engine

Beau de Rochas wrote a paper on fundamentals principle of efficient operation of

piston combustion engine in 1862

To achieve maximum expansion ratio, it is required to maintain maximum pressure

at the beginning of expansion process

theoretical knowledge was adopted by Nikolaus August Otto to built practical four

stroke spark ignition engine

1873: The Brayton engine

George Bailey Brayton Brayton Gas engine

gas engine version in which gas-air mixture is compressed 4 to 5.5 bar into a

receiver and then burnt at constant pressure

efficiency is low because of high heat and mechanical friction losses

Fuel consumption was higher than that of the Otto-Langen atmospheric gas engine

Brayton cycle or Joule cycle is used in gas turbine engine process

1885: The Atkinson Engine

Atkinson engine

engine which used a short stroke for induction and compression and a longer stroke for

expansion and exhaust

one cylinder as against of two of Brayton engine and complex linkage mechanism

modern automobile engine e.g. hybrid electric application (Toyota Prius) and non-

hybrid vehicles with variable valve timing diagram

1892: The Diesel Engine

Rudolf Diesel First diesel engine

compression ignition oil engine was developed by German engineer, Rudolf Diesel in

1892

first experiment air alone get compressed in compression stroke and coal dust is

injected into combustion chamber to initiate combustion

liquid fuel was injected to avoid explosion arise due to coal dust

slow speed diesel engine follows diesel cycle whereas high speed diesel engine adopts

combustion process of Otto and diesel engine

1881: Two Stroke Engine (Clerk’s Engine)

Dugald Clerk Clerk’s two cycle engine

desirability of having one working stroke in every revolution led to the development of

two stroke engine

Separate cylinder was utilised for slight compression of charge

1957: Wankel Engine

Dr. Felix Wankel Wankel engine

basic design that led to the eventual development of the first successful rotary engine

Engine has three lobe rotor and the three separate volumes trapped between the rotor

and casing

Major problem in this engine are: Sealing, seal wear and heat transfer

Common application of Internal combustion engine is listed in given table with their service point of view

and approximate engine power range in each type of service.

SI= spark ignition, D=diesel engine, A=Air cooled, W=water cooled

Source: John B. Heywood, “Internal Combustion Engine Fundamentals”

Different components of IC engine

Main components of reciprocating IC engines

main part of the engine inside which piston reciprocates

ordinary engine is made of cast iron and heavy duty engines are made of steel alloys or

aluminum alloys

In the multi-cylinder engine, the cylinders are cast in one block known as cylinder block.

Types of block: In-line cylinders, Horizontal opposed cylinders, V-banked cylinders

Cylinder:

Fig: In-line cylinder block

Application of In-line cylinder arrangement:

1) Commonly used is in-line 4 cylinder or straight 4 (S4) engine

2) S6 engines are used in BMW, Ford, Jeep, Chevrolet, GMC, Toyota, Suzuki and

Volvo

3) Aviation use: Stampe SV.4, Tiger moth

4) motorcycle engines are configured as singles, parallel twins (British motorcycles:

500 CC Sunbeam S7 & S8), triples (Yamaha XS750, BMW K75, Kawasaki KR750,

Suzuki TR750 transverse 3s, and Proton/Modenas KR3, Honda NS500 V-3s), fours

(Gilera 500 Rondine, Honda CB750) and sixes (1,047 cc Honda CBX,

1,300 cc Kawasaki KZ1300, BMW K1600GT and K1600GTL)

Fig: Horizontal opposed piston with cylinder block

Application:

1) Petrol and diesel opposed-piston engines have been used, mostly in

large scale applications such as ships, aircraft, military tanks and in

factories

2) Diesel Aircraft engine: Junkers Jumo 205

3) submarines: Fairbanks Morse 38 8-1/8 diesel engine,

4) military boats, locomotives: Napier Deltic engine, British Rail Class

55 and British Rail Class 23, Leyland L60, Soviet T-64 tank 5) diesel

truck engines: Commer TS3 three-cylinder

Fig: V-banked cylinders

Application:

1) Vee configuration generally reduces the overall engine length, height and

weight compared with an equivalent inline Configuration

2) V-twin or V-2 engines: used for industrial engines and in several small

cars (Mazda R360)

3) other configurations are: V-3,4,5,6,8,10,12, 14,16,18,20,24

V2 Engine widely associated with motorcycles (installed either transversely or longitudinally), V-twin engines have also been used for industrial

engines and in several small cars. First V-twin engines was built by Gottlieb Daimler in 1889 and was used as a stationary engine

and for boats. Transverse V-twin engines have been used by Harley-Davidson, Ducati and many recent Japanese motorcycles, such

as the Suzuki SV650. Longitudinal V-twin engines have been used by the Honda CX series and several Moto Guzzi motorcycles.

Mazda R360 rear-engined kei car is Mazda V-twin engine and Mazda B360 front-engine light commercial vehicle used a 577 cc

(35.2 cu in) version

V3 Engine V engine with two cylinders in one bank and one cylinder in the other bank. mostly used in two-stroke engines for motorcycles

competing in Grand Prix motorcycle racing. Ex: Honda NS5000/NSR500 Grand Prix racing motorcycles, Honda MVX250F, Honda

NS400R sports bikes

V4 Engine V4 engines are much less common than inline-four engines, however V4 engines have been used at times in automobiles,

motorcycles and other applications. Majority of 2020 MotoGP manufacturers chose the V4 configuration for their bikes e.g. Honda

RC213V, Ducati Desmosedici, KTM RC16, Aprilia - 90° V4 for 2020 season.

V5 Engine V5 engines are very uncommon, with the only production version being the 1997-2006 Volkswagen Group VR5 engine

V6 Engine first V6 prototype engine was produced in 1906. luxury cars with V6 engines produce more vibrations than straight-six engines.

sports cars use flat-six engines instead of V6 engines, due to their lower centre of gravity (which improves the handling). V6 engines

in open-wheeler racing became more common since the early 2010s such as Formula One World Championship switched to

turbocharged V6 engines, FIA Formula 3 Championship (created from the merger of the GP3 Series and the FIA Formula 3

European Championship) began using naturally aspirated V6 engines from 2019

V8 Engine V8 engine was produced by the French company Antoinette in 1904 for use in aircraft. popularity of V8 engines in cars was greatly

increased after introduction of the Ford Flathead V8 in 1932. can be used in motorcycle for motor racing. Typically used in luxury

and racing cars,

V-engine with various configuration

Source: https://en.wikipedia.org/wiki/V-twin_engine

V10 Engine Several V10 diesel engines have been produced since 1965, and V10 petrol engines for road cars were first produced in 1991 with

the release of the Dodge Viper.

V12 Engine two banks of six cylinders are arranged in a V configuration around a common crankshaft. V12 engine built in 1904 for use in racing

boats and popularly used in early luxury automobiles, boats, aircraft and tanks. common use of V12 engines in the 21st century has

been marine engines, large stationary engines and European sports/luxury cars. Ex: Liberty L-12 airplane engine, Renault 12Dc

airplane engine, Rolls-Royce Merlin airplane engine, Lamborghini 350 GT car, Jaguar V12 engine sports car, Mercedes-Benz 600

SE luxury sedan etc.

V14 Engine 14 cylinders mounted on the crankcase in two banks of seven. used on large medium-speed diesel engines used for power

generation and marine propulsion. Cruise Ship: MAN V14 installed in Explorer Dream and Norwegian Spirit

V16 Engine straight 8 banks are balanced. rarely used in automobiles because V8s or V12s of the same displacement. few V16s that have been

produced were used in high-end luxury and high-performance automobiles due to their smoothness (low vibration). common

applications for V16 engines are railroad locomotives, marine craft, and stationary power generators

V18 Engine rare configuration not used in automobiles, large V18 diesel engines have seen limited use in mining, electricity generation, rail

transport, and marine propulsion. Haul truck (Belaz 75600, Liebherr T 282B, Komatsu 960E-1), Diesel-electric locomotives (MLW

M640)

V20 Engine arranged in two cylinder banks of 10, not found in production cars, used in some diesel locomotives, haul trucks, generators and

marine applications. Mercedes-Benz has produced V20 diesel engines used in marine applications. MB 501, MB 511, and the MB

518. Caterpillar_797F for haul truck and EMD_F125 for locomotive produced by Caterpillar Inc.

V24 Engine V engine with 24 cylinders, suitable only for very large trucks or locomotives, formed by coupling multiple smaller engines together

Source: https://en.wikipedia.org/wiki/V-twin_engine

Contd..

Cylinder head:

top end of the cylinder is covered by cylinder head over which inlet and exhaust valve; spark

plug or injectors are mounted

Automotive 4-stroke engine head designs are based on different valve and camshaft

configuration such as Single overhead camshaft, Double overhead camshaft, overhead valve,

side valve, Inter over exhaust, loop flow type, off set cross-flow, in-line cross flow type

Fig: Cylinder head Fig: Exploded view of the engine

Piston:

Fig: Parts of Piston

Transmit the force exerted by the burning of charge to

the connecting rod

sustain mechanical and thermal stress

In case of very high thermal or mechanical stress, the

piston is the first component to fail (compared to engine

block, valves, cylinder head).

made of aluminium alloy which has good heat

conducting property and greater strength at higher

temperature

different types of pistons as per its shape of piston crown

such as: flat top, domed, wedge and dished

Types of piston as per crown design:

Modern piston types:

Piston rings:

Fig: Details of piston ring

Housed in the circumferential grooves

provided on the outer surface of the piston

2 types of rings- compression and oil rings

Compression ring is upper ring of the

piston which provides air tight seal to

prevent leakage of the burnt gases into the

lower portion. Oil ring is lower ring which

provides effective seal to prevent leakage

of the oil into the engine cylinder

Connecting rod:

Converts reciprocating motion of the piston into circular motion of the crank

shaft, in the working stroke

Connects piston and crankshaft by means of pin joints

Crankshaft:

Converts the reciprocating motion of the piston into the rotary motion with the help

of connecting rod

supported in main bearings

consists of eccentric portion called crank

special steel alloys, forging steel, spheroidal graphitic, nickel alloy castings

materials are used for the manufacturing of the crankshaft

Crank case:

It houses cylinder and crankshaft of the

IC engine and also serves as sump for the

lubricating oil

Materials used for crank case are like

aluminium alloy (higher thermal

conductivity), pressed steel sheet

Valves:

Poppet valves controls the timing and quantity of gas

or vapor flow into an engine.

consists of a round head, a stem and a groove at the

top of the valve

Proper timing of the opening and closing of the

valves is required for smooth operation of an engine

variations include two stem solid stem valve, hollow

head engine valve and hollow stem engine valve

Valve can also be designed with different head

shapes such as oval, flat, concave and recessed head.

Hollow head engine valve:

extension of the classic sodium-

filled hollow valve, with an

additional cavity in the valve

head. It can sustain the

temperature peaks in the valve

head and further increase the

valve service life.

Hollow stem engine valve: An

internally cooled construction has

a hollow stem containing a

coolant such as metallic sodium

or sodium-potassium mixture and

is commonly used in extreme

duty and high-performance

exhaust valves.

Contd..

Cam Shaft:

Fig: Camshaft arrangement

used to open and close the valves and made of

cast iron or forged steel with one cam per

valve

Camshafts are gear, belt, or chain driven

In four stroke cycle engines, camshafts turn at

one-half the crankshaft speed.

Camshaft location: e.g. in in-head valve

engines, the camshaft placed at the side along

with a push rod and rocker arm. In some cases,

camshafts are mounted over the head with

cams acting either directly or through a

pivoted follower on the valve

Spark Plug:

In SI engine, spark plug mounted on cylinder head

and used to deliver electric current from an ignition

system to the combustion chamber for igniting of

compressed fuel/air mixture by an electric spark

central electrode tip can be made of copper, nickel-

iron, chromium or noble metals

Spark plug can go up to maximum 45,000 volts and

supply higher current during discharge process,

resulting in a hotter and longer-duration spark

temperature of spark channel may reach to 60,000 K

Spark plugs in automobiles generally have a gap between 0.6 and 1.8 mm (0.024 and

0.071 in)

Fuel Injector:

For atomisation and vaporisation of diesel fuel, fuel

injectors are used in diesel engine

Fuel injector opens and sprays the pressurised fuel

into the engine

It operates with pulse width and inject proper

amount of fuel

Injectors are widely used in such diesel

equipment as railroad locomotives, trucks, buses,

earth movers, ships, and stationary power plants

and are sometimes found in aircraft and motor

truck spark-ignition engines

Flywheel:

Rotating big wheel mounted on the

crankshaft which stores the rotational or

kinetic energy.

Its position is between the engine and

clutch patch to the starter

Serves reservoir which stores energy

during power stroke when excess and

releases stored energy during idle stroke

Controls the speed variations caused by

the fluctuation of the engine turning

moment during each cycle of operation

Flywheel supplies the inertia required to

prevent loss of engine speed and possible

stoppage of crankshaft rotation between

combustion intervals

Terminology used in IC engine

Bore (D): The nominal inner diameter of the working cylinder

Piston area (A): The area of circle of diameter equal to the

cylinder bore

Stroke (L): The nominal distance through which a working

piston moves between two successive reversals of its direction

of motion

Bottom dead centre (BDC): Dead centre when the piston is

nearest to the crankshaft

Top dead centre (TDC): Dead centre when the position is

farthest from the crankshaft

• Displacement volume or swept volume (Vs): The nominal volume generated by the

working piston when travelling from the one dead centre to next one and given as,

Vs=A × L=𝜋

4𝐷2 × 𝐿

Cubic centimetres (cc or cm3) equivalent to millilitres or Litres

Many automobile manufacturers have adopted Variable displacement technology in

large, multi-cylinders engine for improved fuel economy

• Clearance volume (Vc): nominal volume of the space on the combustion side of the

piston at the top dead centre

• Cylinder volume (V): Total volume of the cylinder.

V= Vs + Vc

• Compression ratio (r): 𝑟 =V

Vc

Classifications of IC Engine

Basic engine design

Reciprocating engine (in-line, V, radial, opposed etc.) and

rotary engine (Wankel engine: single or two rotor)

Working cycle

Otto cycle (Spark ignition engine or petrol engine)

Diesel cycle (compression ignition engine or diesel engine)

Number of strokes

Four-stroke engine-naturally aspirated (admitting atmospheric air), supercharged (admitting

pre-compressed fresh mixture), turbocharged (admitting fresh mixture compressed in a

compressor driven by an exhaust turbine), two stroke engine-crankcase scavenged

Fuel:

Gasoline, Diesel oil, compressed natural gas, Liquified petroleum gas (LPG), alcohols

(methanol, ethanol or butanol, biodiesel, dual fuel or multi-fuel engines

Contd..

Fuel supply and mixture preparation

carburetted type, Injection type (port fuel injection or IDI, direct injection)

Method of Ignition

Spark ignition (conventional petrol engine where mixture is uniform and stratified charge

engines where mixtures are non-uniform),

Compression engine (conventional diesel engine, as well as gas engine by pilot injection

of fuel oil), battery or magneto ignition

Method of cooling

Water cooled or air cooled

Cylinder arrangement

In-line or straight, V, Radial, Opposed

Contd..

Combustion chamber design

open chamber (many designs as per piston top: e.g., disc, wedge, hemisphere, bowl in

piston), divided chamber (small and large auxiliary chambers e.g., swirl chambers, pre

-combustion chambers)

Method of load control

Throttling of fuel air flow together so mixture composition is essentially unchanged,

control of fuel flow alone, a combination of these

Valve or port design location

Overhead (I head), side valve (L head), in two stroke engine: cross scavenging, loop

scavenging, uniflow scavenging

Application

Automotive engines, Marine engines, aircraft engines, industrial engines, military engines,

prime movers for electrical generators

Principle of Operation: Four Stroke Engines

• Suction stroke: suction valve

open, exhaust valve closed,

fresh charge admitted

• Compression stroke: both

valves closed, charge

compressed into clearance

volume, P & T increases

• Expansion stroke: both valves

closed, forces piston

downwards, power obtained

• Exhaust stroke: exhaust valve

open, suction valve closed,

burned gases expel out

Principle of Operation: Two Stroke Engines

• No piston stroke for suction and

exhaust operations

• Suction is accomplished by air

compressed in crankcase or by a

blower

• Induction of compressed air

removes the products of combustion

through exhaust ports, therefore no

piston strokes required for suction

and exhaust operations

• Transfer port is there to supply the

fresh charge into combustion

chamber• loop-scavenged engine, end-to-end scavenged or

uniflow scavenged two stroke engines

Comparison of Four-stroke and two-stroke engines

Four-stroke engines Two-stroke engines

1. Four stroke of the piston and two revolution of crankshaft Two stroke of the piston and one revolution of crankshaft

2. One power stroke in every two revolution of crankshaft One power stroke in each revolution of crankshaft

3. Heavier flywheel due to non-uniform turning movement Lighter flywheel due to more uniform turning movement

4. Power produce is less Theoretically power produce is twice than the four-stroke

engine for same size

5. Heavy and bulky Light and compact

6. Lesser cooling and lubrication requirements Greater cooling and lubrication requirements

7. Lesser rate of wear and tear Higher rate of wear and tear

8. Contains valve and valve mechanism Contains ports arrangement

9. Higher initial cost Cheaper initial cost

10. Volumetric efficiency is more due to greater time of induction Volumetric efficiency less due to lesser time of induction

11. Thermal efficiency is high and also part load efficiency better Thermal efficiency is low, part load efficiency lesser

12. It is used where efficiency is important.

Ex-cars, buses, trucks, tractors, industrial engines, aero planes,

power generation etc.

It is used where low cost, compactness and light weight are

important.

Ex-lawn mowers, scooters, motor cycles, mopeds, propulsion

ship etc.

Comparison of SI and CI engine

SI engine CI engine

Working cycle is Otto cycle. Working cycle is diesel cycle.

Petrol or gasoline or high-octane fuel is used. Diesel or high cetane fuel is used.

High self-ignition temperature. Low self-ignition temperature.

Fuel and air introduced as a gaseous mixture in the

suction stroke and get compressed during compression

stroke

Fuel is injected directly into the combustion chamber at high

pressure at the end of compression stroke.

Carburettor used to provide the mixture. Throttle

controls the quantity of mixture introduced.

Injector and high-pressure pump used to supply of fuel.

Quantity of fuel regulated in pump.

Use of spark plug for ignition system Self-ignition by the compression of air which increased the

temperature required for combustion

Compression ratio is 6 to 10.5 Compression ratio is 14 to 22

Higher maximum RPM due to lower weight Lower maximum RPM

Maximum efficiency lower due to lower compression

ratio

Higher maximum efficiency due to higher compression ratio

Lighter Heavier due to higher pressures

Theoretical Valve timing diagram

Fig: Theoretical valve timing diagram

Exact moment at which the inlet and outlet

valve opens and closes with reference to the

position of the piston and crank shown

diagrammatically is known as valve timing

diagram

In theoretical cycle, inlet and exhaust valve

open and close exactly at the dead centre

suction and compression stroke completed

in one revolution of the crankshaft. i.e.

360° of crankshaft rotation.

Expansion and exhaust completed in 360°

of crankshaft rotation

Four processes are completed in 720° of

crankshaft rotation i.e. two revolution of

crankshaft

Actual Valve Timing Diagram

Mechanical Factor:

Clearance between cam, tappet and valve must be slowly taken up to avoid noise and

wear.

“bounce” on its seat

Dynamic factor:

In actual valve timing, the opening and closing of the valves taking into consideration due to

dynamic effects of gas flow.

Inlet Valve Timing:

SI engine intake valve opens 10ᵒ TDC on the exhaust stroke to insure that the valve is

fully open

Inertia of entering fresh charge tends to continue to move into cylinder-ram effect.

Intake valve should not open for too long after BDC

time for opening and closing of intake valve is decided by the speed of the engine.

At very high speeds, fluid friction hampers the advantage of ram effect.

For a variable speed engine, the intake valve opening and closing are a compromise

between the low and high-speed engine

Exhaust Valve Timing:

The pressure in cylinder after first portion of expansion stroke is above atmospheric

pressure which may increase the work required to expel burnt gas. If exhaust valve is

opened some degree before of BDC, then pressure reduces near the end of power stroke.

Valve overlap

Both the intake and exhaust valves are open

Valve over-lap is 15ᵒ in low speed SI engine and 30ᵒ in high speed SI engine

It increase the volumetric efficiency, power output of the engine

Fig: Actual valve timing diagram for low and high-speed SI

engine

Fig: Actual valve timing diagram for

4-strokes diesel engine

Fig: Port timing diagram for 2-stroke engine

Port Timing Diagram

-Drawn for 2-stroke engine

-No valve arrangement

-3 ports- inlet, transfer and exhaust

Working cycle

Otto cycle:

Fig: P-V and T-S diagrams of Otto cycle

Process 1-2: reversible adiabatic compression process, isentropic

s1=s2.

Process 2-3: heat is added at constant volume, state of air changes from

point 2 to 3, complete combustion,

combustion efficiency 100%

Process 3-4: Reversible adiabatic expansion process,

hence isentropic, s3=s4

Process 4-1: heat is rejected by gases at constant volume

Heat supplied, qs=Cv(T3-T2)

Heat rejection, qR=Cv(T4-T1)

Compression ratio, 𝑟𝑘=𝑉1

𝑉2

Thermal efficiency, 𝜂𝑡ℎ =𝑞𝑠−𝑞𝑅

𝑞𝑠=

Cv T3−T2 −Cv T4−T1Cv T3−T2

= 1 −T4−T1T3−T2

In process 1-2, adiabatic compression process,

𝑇2𝑇1=

𝑉1𝑉2

𝛾−1

=> 𝑇2 = 𝑇1. 𝑟𝑘𝛾−1

In adiabatic expansion process, i.e. 3-4,

𝑇4𝑇3

=𝑉3𝑉4

𝛾−1

=𝑉2𝑉1

𝛾−1

=> 𝑇3 = 𝑇4. 𝑟𝑘𝛾−1

𝜂𝑡ℎ = 1 −𝑇4 − 𝑇1

𝑇4. 𝑟𝑘𝛾−1 − 𝑇1. 𝑟𝑘

𝛾−1 = 1 −1

𝑟𝑘𝛾−1

Work done (W)

Pressure ratio, 𝑟𝑝=𝑃3

𝑃2=

𝑃4

𝑃1𝑃2

𝑃1=

𝑃3

𝑃4=

𝑉1

𝑉2

𝛾= 𝑟𝑘

𝛾

Contd..

𝑊 =𝑃3𝑉3 − 𝑃4𝑉4

𝛾 − 1−𝑃2𝑉2 − 𝑃1𝑉1

𝛾 − 1

=1

𝛾 − 1𝑃4𝑉4

𝑃3𝑉3𝑃4𝑉4

− 1 − 𝑃1𝑉1𝑃2𝑉2𝑃1𝑉1

− 1

=1

𝛾 − 1𝑃4𝑉1 𝑟𝑘

𝛾−1 − 1 − 𝑃1𝑉1 𝑟𝑘𝛾−1 − 1

=𝑃1𝑉1𝛾 − 1

𝑟𝑝 𝑟𝑘𝛾−1 − 1 − 𝑟𝑘

𝛾−1 − 1

=𝑃1𝑉1𝛾 − 1

𝑟𝑘𝛾−1 − 1 𝑟𝑝 − 1

Mean effective pressure, 𝑃𝑚 =𝑤𝑜𝑟𝑘 𝑑𝑜𝑛𝑒

𝑆𝑤𝑒𝑝𝑡 𝑣𝑜𝑙𝑢𝑚𝑒=

𝑤𝑜𝑟𝑘 𝑑𝑜𝑛𝑒

𝑉1−𝑉2

𝑃𝑚 =

𝑃1𝑉1𝛾 − 1

𝑟𝑘𝛾−1 − 1 𝑟𝑝 − 1

𝑉1 − 𝑉2=𝑃1𝑟𝑘 𝑟𝑘

𝛾−1 − 1 𝑟𝑝 − 1

(𝛾 − 1)(𝑟𝑘 − 1)

Contd..

Diesel cycle:

Thermodynamic cycle for low speed CI/diesel engine

Fig: P-V and T-S diagrams of Diesel cycle

Process 1-2: Reversible adiabatic compression process, work input

Process 2-3: Heat addition at constant pressure, air expands from v2 to v3 doing

some work. In actual engine heat addition takes place in the form of injection of fuel

which self-ignites due to high temperature caused by high compression ratio, and

burns at constant pressure. At point 3, called the cut off point, heat or fuel supply is

cut off

Process 3-4: Reversible adiabatic expansion process, work done on the piston, work

out put

Process 4-1: at the end of expansion stroke, heat is rejected by gases at constant

volume.

Heat supplied, Q1=Cp(T3-T2)

Heat rejection, Q2=Cv(T4-T1)

Compression ratio, 𝑟𝑘=𝑉1

𝑉2

Cut off ratio, 𝑟𝑐=𝑉3

𝑉2

Thermal efficiency, 𝜂𝑡ℎ =𝑄1−𝑄2

𝑄1=

𝐶𝑝(𝑇3−𝑇2)−𝐶𝑣(𝑇4−𝑇1)

𝐶𝑝(𝑇3−𝑇2)= 1 −

1

𝛾

(𝑇4−𝑇1)

(𝑇3−𝑇2)

Contd..

𝜂𝑡ℎ = 1 −1

𝛾

൯(𝑇4 − 𝑇1

൯(𝑇3 − 𝑇2= 1 −

1

𝛾. 𝑟𝑘 𝛾−1

𝑟𝑐𝛾 − 1

𝑟𝑐 − 1

Cut-off ratio should not more than 10% of the stroke as smoking tends to occur in an actual engine

Work done (W)

𝑊 = 𝑃2 𝑉3 − 𝑉2 +𝑃3𝑉3−𝑃4𝑉4

𝛾−1−

𝑃2𝑉2−𝑃1𝑉1

𝛾−1

= 𝑃2 𝑟𝑐𝑉2 − 𝑉2 +𝑃2𝑟𝑐𝑉2−𝑃4𝑟𝑘𝑉2

𝛾−1−

𝑃2𝑉2−𝑃1𝑟𝑘𝑉2

𝛾−1since 𝑉4 = 𝑉1

= 𝑃2𝑉2𝑟𝑐−1 𝛾−1 + 𝑟𝑐−𝑟𝑐

𝛾.𝑟𝑘−𝛾.𝑟𝑘 − 1−𝑟𝑘

1−𝛾

𝛾−1

= 𝑃1𝑉1. 𝑟𝑘𝛾−1 𝛾 𝑟𝑐−1 −𝑟𝑘

1−𝛾(𝑟𝑐𝛾−1)

𝛾−1

Mean effective pressure,

𝑃𝑚 =𝑃1𝑉1.𝑟𝑘

𝛾−1 𝛾 𝑟𝑐−1 −𝑟𝑘1−𝛾(𝑟𝑐

𝛾−1)

𝛾−1

𝑉1−𝑉2=

𝑃1𝑟𝑘𝛾 𝛾 𝑟𝑐−1 −𝑟𝑘

1−𝛾(𝑟𝑐𝛾−1)

(𝛾−1)(𝑟𝑘−1)

Dual cycle or limited pressure cycle

Thermodynamic cycle for high speed diesel and hot spot ignition engine

Fig: P-V and T-S diagrams of Dual cycle

Process 1-2: Reversible adiabatic compression process, work input

Process 2-3: Heat addition at constant volume tends to increase thermal efficiency

Process 3-4: Heat addition at constant pressure limits the maximum pressure

Process 4-5: Reversible adiabatic expansion process, work done on the piston,

work out put

Process 5-1: at the end of expansion stroke, heat is rejected by gases at constant

volume.

Total heat supplied, Q1= Cv(T3-T2)+ Cp(T4-T3)

Heat rejection, Q2=Cv(T5-T1)

Compression ratio, 𝑟𝑘=𝑉1

𝑉2

Cut off ratio, 𝑟𝑐=𝑉4

𝑉3

Pressure ratio, 𝑟𝑝=𝑃3

𝑃2

𝜂𝑡ℎ = 1 −(𝑇5−𝑇1)

(𝑇3−𝑇2)+𝛾(𝑇4−𝑇3)= 1 −

1

𝑟𝑘𝛾−1

𝑟𝑝. 𝑟𝑐𝛾−1

𝑟𝑝−1 +𝛾𝑟𝑝(𝑟𝑐−1)

Work done (W)

𝑊 = 𝑃3 𝑉4 − 𝑉3 +𝑃4𝑉4 − 𝑃5𝑉5

𝛾 − 1−𝑃2𝑉2 − 𝑃1𝑉1

𝛾 − 1

= 𝑃3𝑉3 𝑟𝑐 − 1 +(𝑃4𝑟𝑐𝑉3 − 𝑃5𝑟𝑘𝑉3) − (𝑃2𝑉3 − 𝑃1𝑟𝑘𝑉3)

𝛾 − 1

=𝑃1𝑉1. 𝑟𝑘

𝛾−1 𝛾𝑟𝑝(𝑟𝑐 − 1) + 𝑟𝑝 − 1 −. 𝑟𝑘𝛾−1 (𝑟𝑝𝑟𝑐

𝛾 − 1)

𝛾 − 1

Mean effective pressure,

𝑃𝑚=

𝑃1𝑉1. 𝑟𝑘𝛾−1 𝛾𝑟𝑝(𝑟𝑐 − 1) + 𝑟𝑝 − 1 −. 𝑟𝑘

𝛾−1 (𝑟𝑝𝑟𝑐𝛾 − 1)

𝛾 − 1

𝑉1 − 𝑉2

=𝑃1𝑟𝑘

𝛾 𝑟𝑝(𝑟𝑐 − 1) + 𝑟𝑝 − 1 −. 𝑟𝑘1−𝛾 (𝑟𝑝𝑟𝑐

𝛾 − 1)

𝛾 − 1 𝑟𝑘 − 1

Contd..

Comparison of Otto, Diesel and Dual cycle:

(a) For same compression ratio and same heat input

𝜂𝑡ℎ 𝑂𝑡𝑡𝑜 > 𝜂𝑡ℎ 𝐷𝑢𝑎𝑙 > 𝜂𝑡ℎ 𝐷𝑖𝑒𝑠𝑒𝑙

(a) For constant maximum pressure and same heat input

𝜂𝑡ℎ 𝐷𝑖𝑒𝑠𝑒𝑙 > 𝜂𝑡ℎ 𝐷𝑢𝑎𝑙 > 𝜂𝑡ℎ 𝑂𝑡𝑡𝑜

(a) For same maximum pressure and temperature

𝜂𝑡ℎ 𝐷𝑖𝑒𝑠𝑒𝑙 > 𝜂𝑡ℎ 𝐷𝑢𝑎𝑙 > 𝜂𝑡ℎ 𝑂𝑡𝑡𝑜

(a) For same maximum pressure and output

𝜂𝑡ℎ 𝐷𝑖𝑒𝑠𝑒𝑙 > 𝜂𝑡ℎ 𝑂𝑡𝑡𝑜

Contd..

Text Books:

T1. M.L. Mathur and R.P. Sharma, “Internal Combustion Engine”, Dhanpat Rai Publications, Revised Edition, India.

T2. V.Ganesan, “Gas Turbines”, Tata McGraw Hill Education Pvt. Publication, Third Edition.

Reference Books:

R1. John B. Heywood, “Internal Combustion Engine Fundamentals”, McGraw- Hill Education-publisher.

Website collection:

https://www.mpoweruk.com/heat_engines.htmhttp://www.fem.unicamp.br/~em313/paginas/consulte/steame.htmhttps://en.wikipedia.org/wiki/Stirling_enginehttp://annals.fih.upt.ro/pdf-full/2003/ANNALS-2003-3-21.pdfhttps://en.wikipedia.org/wiki/V_enginehttps://x-engineer.org/automotive-engineering/internal-combustion-engines/ice-components-systems/internal-combustion-engine-piston/http://grounds-mag.com/mag/grounds_maintenance_understanding_overheadvalve_engines/https://dieselnet.com/tech/air_ports.phphttps://en.wikipedia.org/wiki/Spark_plughttps://www.slideshare.net/BhagyashriDhage/flywheel-89354644https://extrudesign.com/valve-timing-diagram-in-four-stroke-engines/